Dynamic variation of hemodynamic shear stress on the walls of developing chick hearts: computational models of the heart outflow tract
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Heart morphogenesis and growth are influenced by hemodynamic forces (wall shear stress and blood pressure) acting on the walls of the heart. Mechanisms by which hemodynamic forces affect heart development are not well understood, in part because of difficulties involved in measuring these forces in vivo. In this paper, we show how wall shear stress in the heart outflow tract (OFT) of chick embryos at an early developmental stage (HH18) are affected by changes in the geometry and motion of the OFT wall. In particular, we were interested in the effects of cardiac cushions, which are protrusions of the OFT wall toward the lumen and that are located where valves will later form. We developed idealized finite element models (FEM) of the chick OFT with and without cardiac cushions. Geometrical parameters used in these models were estimated from in vivo images obtained using optical coherence tomography (OCT) techniques. The FEMs showed significant reverse blood flow (backflow) in the OFT, consistent with experimental observations in the chick heart at HH18, and revealed that cardiac cushions decrease backflow. In addition, our FEMs showed that the spatial distribution of wall shear stress is affected by cardiac cushions, with larger absolute peak values observed at the cushions. Differences in mechanical stimuli (wall shear stress) that the cells in the cardiac cushions and elsewhere are subjected to may affect valve formation and heart development.